Noncontact Large-Scale Displacement Tracking: Doppler Radar for Water Level Gauging

Doppler radar has been used for small-scale displacement detection, e.g. respiration and heartbeat. The motion amplitude is less than half a carrier wavelength. In this letter, a novel Doppler radar technique is presented for accurate tracking of large-scale displacement of several carrier wavelengths, e.g., the water level variation. The DC-coupled architecture is used to ensure precise measurement of slow motions even with stationary moment. A novel signal processing approach is proposed to increase the demodulation linearity to deal with inconstant signal amplitude, dynamic dc offset and phase ambiguity in large-scale displacement tracking. Experiments have been carried out in the outdoor environment to monitor the relative water level position in a rain barrel when the water was pumped in or drained out. It is shown that the proposed technique can accurately gauge the relative water level variation of 3.5 wavelengths with mm accuracy.